DNA Part 1: The basics

Review DNA Gene Protein Trait

So far... The Big Picture Physical traits come from heredity DNA → Genes → Proteins → Traits Physical traits come from heredity Chargraff’s Data Ratios of DNA molecule => A:T & G:C always close to 1:1 Different percentages for different species leading to different traits

What is DNA? DNA is a special molecule long chains linking four subunits (smaller molecules) sequence “encodes” genetic information

What’s that DNA stuff made of? Wait on Notes DNA = deoxyribonucleic acid The DNA chain is made of many nucleotides joined together (a polymer). Nucleotides (a monomer)= molecules with a sugar portion (the “deoxy” form of ribose) [same] a phosphate group [same] a nitrogen base [4 different] Main Idea? Key Details?

The 4 nitrogen bases of DNA are... Adenine Thymine Guanine Cytosine How do I remember? “All Turtles Go Camping” “All Teachers Get Cranky”

DNA Structure

Overall Structure DNA forms into a “double helix,” or a twisted ladder shape The sugar-phosphate backbone forms the “legs” of the ladder The bonds between the sugar and phosphate groups form the twist of the helix The bases paired up between the legs form the “rungs” of the ladder/helix

The Double Helix Weak hydrogen bonds Strong covalent bonds

The 4 Nitrogen Bases of DNA Are... A always pairs with T Forms 2 bonds G always pairs with C Forms 3 bonds This ensures that only correct pairs are formed.

Practice Problem If an organism has a 64% GC content, what percent of A, T, C and G does it have? A = T = G = C = 18 32